SITE 1088

Site 1088 is located on the Agulhas Ridge in the southeast Atlantic Ocean at a water depth of 2083 m. This bathymetric setting places the site near the interface between NADW and CPDW. The primary objective of Site 1088 was to recover a long Cenozoic carbonate sequence that could be used to study paleoceanographic change near the Subtropical Front, which today is located north of the Agulhas Ridge.

Three holes were drilled representing a combined 223.4-m section, consisting predominantly of carbonate microfossils representing sediment deposition from the Holocene to middle Miocene (~13-14 Ma). The sediments recovered are predominantly nannofossil ooze, foraminifer-bearing nannofossil ooze, foraminiferal nannofossil ooze, and nannofossil foraminiferal ooze. Carbonate percentages vary from 85 to 95 wt% and the abundance of foraminifers decreases progressively downhole.

Sedimentation rates averaged 10 m/m.y. in the Pleistocene, 7 m/m.y. in the Pliocene, 17-30 m/m.y. in the late Miocene, and 11 m/m.y. during the middle Miocene. Only two short depth intervals (0-5.5 and 122-129 m composite depth [mcd]) were cored in more than one hole and, as a result, continuity of the sedimentary section could not be documented and a continuous spliced record could not be constructed at Site 1088. Magnetic inclinations were low and less than expected for the site location (60°) and declinations were highly scattered, suggesting drill string remagnetization of the core.

High-resolution samples (one per section) of interstitial waters were taken in Hole 1088B, 1.5-115.9 meters below seafloor (mbsf), for major ion and stable isotopic analysis. Many of the results from these samples must await shore-based analyses, but shipboard analyses show that, as expected, chlorinity increases downhole, with a slight local maximum at about 40 mbsf that probably resulted from diffusion of higher salinity water associated with the last glaciation.

Variations in diffuse spectral reflectance suggest the presence of marine isotope stages (MISs) 1 to 13 in Core 177-1088B-1H in the top 5.5 mbsf. Although the upper Pleistocene sequence is marked by relatively low sedimentation rates (~10 m/m.y.), the record is similar to that from ODP Site 704 to the south (47°S, 7.5°E, 2532 m), and comparison of the two holes will be useful for studying glacial-to-interglacial changes in NADW flux to the Southern Ocean. Sediments recovered at Site 1088 will be useful for studying paleoceanographic change during the Neogene at a temporal resolution of 104 to 105 years. The 140-m section of upper Miocene sediments recovered in Holes 1088B and 1088C is particularly promising in that variations in magnetic susceptibility show evidence of cyclicity in the Milankovitch frequency band. Although a complete composite section was not retrieved, the sediments should provide a detailed record of late Miocene changes in surface- and deep-water circulation.

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